1. Field of the Invention
This invention generally relates to apparatus and procedures for replenishing particulate materials (e.g., bulk catalysts, catalyst additives, particulate raw materials, etc.) for industrial processes (e.g., fluid catalytic processes used to refine petroleum, polymer manufacturing processes, etc.). More particularly, this invention relates to those apparatus and methods calling for injection of particulate materials into industrial processes using streams of high pressure gas (e.g., air, nitrogen, hydrocarbons, etc.) in which the particulate material is entrained.
2. Description of the Prior Art
Particulate materials are employed in many chemical and petrochemical manufacturing processes. Requirements for more closely controlling and adjusting use of such materials can be engendered by any number of anticipated and/or unanticipated changes in such processes, e.g., (1) changing product requirements, (2) changing character of feedstock(s) and/or (3) changing pollution control regulations. Moreover, the ability to more closely control and adjust introduction of particulate materials into most industrial processes serves to minimize the use of, and hence the costs associated with, raw materials, catalysts and energy. The ability to more closely control and adjust industrial processes also usually serves to reduce perturbations to such processes when those pressurized vessels holding raw materials, catalyst, diluents, etc. for use in said processes have to be taken out of service in order to refill them.
Many of those devices and procedures used to replenish particulate materials stored in pressurized vessels that feed into industrial processes call for use of a stream of pressurized gas (usually air) to transfer the particulate material from an unpressurized storage tank to a pressurized process vessel. These materials are then injected into the process by entraining them in another stream of pressurized gas (e.g., air, nitrogen, light hydrocarbon gases, etc.) that feeds into said process.
Unfortunately, significant errors and/or maladjustments were frequently introduced into many industrial processes employing such streams of pressurized gas. Such errors and/or maladjustments generally follow from a combination of two factors: (1) many particulate material delivery systems are controlled by timed meters or clocks and (2) plant air supply systems supplying the streams of pressurized gas may, and often do, operate over a rather wide range of operating pressures. For example, an xe2x80x9cassumedxe2x80x9d 60 psi plant air supply system would, in fact, operate at pressures ranging from about 30 to 80 psi at any given point in time. Such pressure differences caused timed particulate material injection devices using these air streams to deliver differing amounts of particulate material in different time periods in which plant air pressures varied.
The prior art has addressed this problem in several ways. For example, U.S. Pat. No. 5,389,236 (xe2x80x9cthe ""236 patentxe2x80x9d) discloses a catalyst addition system wherein a pressurized catalyst vessel is continuously weighed in order to determine how much catalyst is actually added to a fluid catalytic process in any given time period. In other words, this catalyst injection system operates on the basis of the weight of material actually leaving the vessel and injected into the processxe2x80x94regardless of the pressure of the air stream used to deliver the material to that process. The apparatus and methods of the present patent disclosure build upon the weighing procedures taught in the ""236 patent; hence said patent is incorporated herein by reference.
The advances made through use of the apparatus and processes of the present patent disclosure revolve around the fact that the pressurized vessels used in such processes are typically operated under pressures ranging from about 30 psi to about 150 psi. Therefore, they must be depressurized before new particulate material supplies (e.g., catalysts, raw materials, diluents, etc.) can be loaded into them. Those skilled in this art will appreciate that this reloading is a time-consuming process. For example, using those vessel venting devices and procedures on the catalyst addition systems taught by the ""236 patent, a typical refilling operation (comprised of [1] depressurizing the vessel from an operating pressure ranging from about 30 to about 150 psi, [2] refilling the vessel with particulate material and [3] repressurizing the vessel back to a 30-150 psi operating pressure) may take from about 60 to about 120 minutes for vessels having a capacity for about 10-15 tons of particulate material.
Such rather lengthy time requirements follow, in large part, from the fact that the depressurization process, and especially the first part of that depressurization process, must proceed very slowly. Otherwise, any particulate material still remaining in the vessel (and there usually is some) when it is vented will be entrained in the departing air and lost from the system. This will be especially likely if the initial phase of the vessel depressurization process proceeds too quickly (i.e., so quickly that any significant amount of particulate material in the vessel is, in effect, sucked out of said vessel along with the pressurized gas being vented). Particulate material losses of this kind have at least two bad consequences. First, valuable materials such as catalysts will be wasted; and second, any particulate material entrained in a stream of rapidly released gas through the vessel""s venting system may clog or otherwise interfere with operation of equipment xe2x80x9cdownstreamxe2x80x9d of that venting system (e.g., gas silencers, electrostatic precipitation units, dust-catching bag units, etc.).
There is, however, a competing drawback to venting these pressurized vessels too slowly. This drawback follows from the fact that while such a vessel is being depressurized, refilled with fresh particulate material and again repressurized, it is no longer capable of injecting its particulate material contents into the industrial process it serves. In short, the vessel is xe2x80x9cdownxe2x80x9d while it is being resupplied with particulate material. Consequently, if the process using the particulate material is scheduled to receive a shot or stream of the particulate material during the 60-120 minutes that the vessel is down for its resupply routine, injection of scheduled shot(s) or stream(s) of the material must be deferred until the vessel is again put back into service. Likewise, if the process needs an unscheduled shot or stream of the particulate material, this unscheduled addition also must be deferred until the vessel is again brought back into service. Those skilled in the chemical engineering arts will of course appreciate that the longer a scheduled or needed injection of catalyst or raw material is deferred, the greater the perturbation to most ongoing chemical processes. Hence, there is an ever pressing demand to shorten the time needed to recharge a pressurized vessel whose normal duty is to feed an industrial process with a particulate material at time intervals that are shorter (e.g., every 10 minutes) than the down time (e.g., 45-60 minutes) associated with replenishing the vessel with fresh particulate material. In many cases, if these refill times can not be shortened, very expensive duplicate pressure vessel systems must be employed.
Heretofore, the depressurization aspect of these vessel replenishing operations has been carried out in one of two ways. The first way involves the use of a single xe2x80x9con/offxe2x80x9d type valve (such as a so-called ball type valve) having a very small opening. The second way employs valves that are capable of producing proportional or variable sized openings (xe2x80x9cproportional valvesxe2x80x9d). Use of a single, ball type, valve in such venting operations has the advantage of simplicity of operation and maintenance. Such valves must, however, have a very small vent opening so that an initial, large volume, surge of escaping air does not suck particulate material out of the vessel. Use of such small, ball type, vent valves does, however, imply long decompression times. This follows from the fact that as the pressure decreases, the rate of depressurization also decreases. For example, depressurization of a 10-15 ton catalyst vessel from about 60 psi to atmospheric pressure using a 1.0 inch, ball type, vent valve will usually take from about 30 to about 60 minutes. Obviously, this is a significant portion of the overall 60-120 minute vessel refilling operation associated with vessels of this size.
Proportional valves have the advantage of being able to open very, very slightly in order to initiate a vessel depressurization process in a manner such that only a very small volume of high pressure air is initially allowed to escape. This circumstance prevents particulate material from being sucked out of the vesselxe2x80x94which, here again, would be the case if an initial, large volume, surge of high pressure air were allowed to vent too quickly. As the pressure in a vessel gradually goes down, these proportional valves are opened further and further so that larger and larger volumes of airxe2x80x94at lower and lower pressuresxe2x80x94can be vented without sucking particulate material out of the vessel along with the departing air.
Thus, use of proportional valves generally allows a vessel to be vented more quickly than it could be using a single, small vent size, ball valve. Proportional valves do, however, have certain very significant disadvantages associated with their use. For one thing, they are considerably more complex than ball type valves. Hence they are much more expensive. Worse yet, they also are generally much more difficult to install, operate and maintain. These drawbacks follow in part from the fact many industrial valves (proportional type valves as well as ball type valves) are mechanically driven by fluid pressure systems (air pressure systems, hydraulic systems and the like). Thus, once a CPU gives an order (an electrical signal) to open or close a valve, it is inherently much more difficult for a fluid pressure system to take that signal and convert it into a very slight adjustment in the size of a vent opening in a proportional valve than it is for the very same fluid pressure system to create the more decisive on/off action in a ball type valve whereby said valve is either fully opened or fully closed. Moreover, use of proportional valves implies that any CPU used to control operation of that proportional valve must be able to receive and give xe2x80x9cproportionalxe2x80x9d type electrical signals rather than simple on/off type signals. Indeed, because of the nature and magnitude of the problems associated with the use of proportional valves in particulate material injection processes, many industrialists, and especially petroleum refiners, generally prefer to use the more reliable, single ball valve-based, venting technique and xe2x80x9clive withxe2x80x9d the longer time periods they take to depressurize a vessel.
In response to the tradeoff problems associated with entraining particulate material in an air stream that is too quickly vented from a vesselxe2x80x94versus taking inordinately long periods of time to refill those vessels, and thereby perturbing the industrial process being fed by said vesselsxe2x80x94applicant has developed certain apparatus and procedures for more quickly replenishing those vessels whose main duty is to supply particulate materials to an ongoing industrial process. These apparatus and procedures take shorter time periods to vent the vessel (e.g., 5-10 minutes to vent a 10-15 ton catalyst vessel as opposed to the 30-60 minutes needed to vent the same vessel using single ball valve based venting operations). Use of applicant""s apparatus and procedures also avoids the above-noted proportional signal based problems associated with using proportional valves.
To these ends, applicant""s apparatus and procedures employ two or more, on/off type, vent valves of different sizes. These vent valves can be sized such that the operating pressure in a particle containing vessel will be gradually released, in low volumes, when the vessel is initially depressurized. Thereafter, the pressurized gas can be released in larger volumes when a predetermined lower pressure is reached and thereby speed up the overall depressurization process. That is to say that, after an initial first phase depressurization operation is completed through use of a first, relatively smaller, on/off type vent valve (e.g., a ball valve having a 1.0 inch vent diameter), a second, on/off type valve, of larger diameter (e.g., a ball valve having a 3.0 inch vent diameter) is opened to release larger volumes of the pressurized gas in a second phase of an overall depressurization process. Release of these larger volumes of gas at the lower pressures extant in this second phase of the depressurization process serves to shorten the overall time needed to depressurize the vessel (again, relative to use of a single, on/off type valve venting system). Consequently, the operational advantages associated with the use of on/off type valves can be gained and the decompression periods shortenedxe2x80x94without the need for a CPU having the ability to process proportional type electrical signals in order to partially open a proportional valve. In one particularly preferred embodiment of this invention, the first depressurization phase is carried out using a first, ball type, vent valve whose air passage is at least 50% smaller in inside air passage diameter than a second, ball type, vent valve used in the second phase of the depressurization process. In many cases the first vent valve will be 90% smaller than the second vent valve. In one particularly preferred embodiment of this invention, the first vent valve will continue with its venting function during the second phase of the venting process. Again, in most cases, the second venting phase will not commence until the first venting phase has lowered the vessel pressure by at least 50% (e.g., from 60 psi to 30 psi).
In yet another preferred embodiment of this invention, upon being refilled with particulate material, the vessel will be repressurized using a first, relatively large, injection valve system and a second, relatively small (i.e., relative to the first injection valve), gas injection valve system. The main function of this first, relatively large, injection valve system will, however, be to deliver particulate material to the vessel. That is to say that the particulate material is delivered to the vessel entrained in an air stream sent to said vessel via the first, relatively larger valve. The particulate material xe2x80x9cfalls outxe2x80x9d of this air stream when it changes direction in the vessel and is vented out of said vessel. Thereafter, this relatively large first injection valve system can be used to deliver pressurized air (which is then not carrying particulate material with it) to the vessel in order to help repressurize said vessel. In another preferred embodiment of this invention, both the first and second injection valve systems are employed to bring the vessel to a predetermined first repressurization level (e.g., 50 psi) while only the second, gas injection valve system is used to bring the vessel pressure from the first predetermined first repressurization level (e.g., 50 psi) to a second (and usually final) operating pressure (e.g., 60 psi). In any case, the main function of the second, relatively smaller, gas injection valve is to deliver a relatively smaller stream of air (relative to that delivered by the first relatively larger, injection valve) to the vessel in order to bring the vessel to the second (and usually final) predetermined operating pressure (e.g., a 60 psi operating pressure for a 10-15 ton vessel). This repressurization procedure serves to prevent the first relatively large valve system from xe2x80x9covershootingxe2x80x9d the desired final operating pressure (e.g., 60 psi). This overshooting can follow from the fact that larger valves generally have longer signal response times than smaller valves. The second, smaller injection valve also is better able to make certain hereinafter more fully described ongoing adjustments in the vessel""s operating pressure.
Next, it should be noted that this second, relatively small, gas injection valve could be connected to the vessel in conjunction with a mechanical pressure regulator; and such a mechanical pressure regulator could be used to independently control the vessel""s pressure. In which case, the CPU controlling the apparatus and processes of this patent disclosure would not be needed to detect the operating pressure in the vessel. That is to say that a mechanical pressure regulator could be adjusted locally by the operator. Indeed, in many prior art vessel repressuring systems, a ball valve was used in conjunction with a pressure regulator in repressuring procedures wherein the ball valve was opened and the pressure regulator allowed air pressure into the vessel until it reached a given set point (e.g., 60 psi). Applicant has, however, found that use of such a mechanical pressure regulator for this purpose is less preferred in the apparatus and processes of this patent disclosure. This preference follows from the fact that mechanical pressure regulator set pressures (e.g., 60 psi) could be inadvertently adjusted to levels slightly below the pressure that a CPU is xe2x80x9clooking forxe2x80x9d; consequently, the CPU will not restart particulate material additions because the sought after pressure will not be high enough.
Therefore, in some of the more preferred embodiments of this invention, a mechanical pressure regulator will not be employed to permanently set the vessel""s operating pressure. Instead, such a pressure regulator will be replaced with a pressure transmitter that is in continuous communication with the CPU that controls the apparatus and procedures of this patent disclosure. Thus, in this preferred embodiment, applicant""s CPU will need to be modified, in ways known to those skilled in this art, to enable it to read the vessel""s pressure using signals generated by the pressure transmitter. This pressure transmitter can be used to continuously monitor and adjust the vessel""s operating pressure. In the most preferred embodiments of this invention, a desired operating pressure in a vessel (e.g., 60 psi) will be detected by the pressure transmitter and maintained by a logic program in the CPU. This logic program is, most preferably, set up to control the pressure in the vessel in a manner similar to the way a central heating controller in a home heating system controls the home""s temperature. That is to say, such home heating systems are either xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d as the temperature falls below or raises above a set level temperature (e.g., 68xc2x0 F.).
When using such an on/off control system in the processes of this patent disclosure, if the pressure in the vessel falls a predetermined amount below, e.g., about 3% below, a given setpoint (e.g., 3% below a 60 psi operating pressure), a valve controlling the pressurized air supply to the vessel is opened by a signal from the CPU. For example, when such a pressure transmitter informs the CPU that the vessel pressure has fallen to the prescribed level (e.g., 58.2 psi or 3.0% of 60 psi), the relatively smaller gas injection valve of applicant""s apparatus will be opened. When the pressure reaches another higher predetermined pressure, e.g., about 3% above the set pressure (61.8 psi or 3% of 60 psi), the valve will be shut off.
Thus, the apparatus and procedures of this patent disclosure are generally characterized by their use of (1) a computer control unit, (2) at least one weighing device such as a load cell to determine the amount of particulate material in a pressurized vessel and thereby determine when a vessel recharge signalxe2x80x94generating amount of the particulate material has been reached, (3) two separate and distinct venting valves, of different size, that each operate on an on/off mode of operation (e.g., ball type valves) and, optionally, (4) use of two injection valves, of different size, to repressurize the vessel and, optionally, (5) use of a pressure transmitter and an on/off logic program in the CPU to maintain the pressure in said vessel at some predetermined operating pressure.
Again, the hereindescribed apparatus and procedures are generally applicable to venting pressure vessels containing any fluidizable, solid particles, but they are especially useful in adding particulate catalyst materials to those FCC processes used to refine petroleum. Hence, particles of this type, used in this exemplary industrial process, have been and will be used to illustrate the inventive concepts of this patent disclosure. Consequently, for the purposes of this patent disclosure, the terms xe2x80x9ccatalystxe2x80x9d or xe2x80x9ccatalyst particlexe2x80x9d should be taken in a broader sense to mean any fluidizable particulate material. Similarly the terms xe2x80x9cFCC unitxe2x80x9d or xe2x80x9cFCC processxe2x80x9d should be taken in a broader sense to mean any industrial process into which a particulate material is injected. In much the same vein, the term xe2x80x9cairsxe2x80x9d should be taken to mean any other gas such as nitrogen, hydrocarbon gases, etc. that are commonly used to entrain particulate materials in any industrial process wherein such particles are employed. And finally, for the purposes of this patent disclosure, the terms xe2x80x9cvalvexe2x80x9d or xe2x80x9cvalve systemxe2x80x9d should be taken to imply the piping system that is connected to any given valve.